1. Field of the Invention
The invention disclosed herein relates generally to a proportioning pump assembly, and more particularly to a pumping apparatus that maintains the ratio of two pumped fluids, which ratio is unaffected by alterations in the pressure and velocity of the flowing fluids.
2. Background of the Prior Art
Several devices have been developed for injecting predetermined quantities of liquid additives into a liquid flow stream. For example, beverage dispensing valves that provide for the mixing of carbonated water and syrup to produce a dispensed beverage are well known in the art. Other applications such as adding medication to drinking water with such additives as chlorine or iodine and adding fertilizer concentrate to irrigation water are similarly well know.
A number of fluid pumps have been designed which inject an additive into the primary fluid stream where the primary fluid provides the motive fluid for activating the additive injection pump. For example, U.S. Pat. No. Re. 35,780 to Hassell et al. discloses a beverage dispensing valve having two sets of oval gears in which the ratio of two liquid beverage constituents is maintained by the interaction of the oval gear pairs, which are sized so that the desired ratio is maintained. Flow is regulated through use of solenoid operated pallet valves for each liquid component.
U.S. Pat. No. 3,821,963 to Olsen et al. discloses a liquid proportioning apparatus for injecting a liquid into the flow of a driving liquid. The apparatus uses an eccentric paddle wheel as the fluid motor to drive a separate pump for a second liquid to be injected into the driving flow.
U.S. Pat. No. 6,357,466 to Walton et al. discloses an apparatus for generating a mixture of a first fluid and a measured quantity of a second fluid in a fluid stream. The gears of a flow meter rotate when a first fluid is passed through the flow meter. A shaft connected coaxially with a gear of the flow meter is connected with a gear of a cavity pump for a second fluid so that a the second fluid is pumped through the cavity pump when the first fluid is directed through the flow meter.
While the above-mentioned compound motor/pump assemblies have been generally satisfactory to enable a driving fluid to be used as the motive force to drive a fluid motor which in turn drives a proportional pump, these devices have not enjoyed significant commercial success. While positive displacement pumps, such as gear pumps, may at times have the capacity to be used as a fluid motor, their design typically enables leakage past the gears between the gear teeth and the housing, and between the gear sidewalls and the housing. For mixing applications requiring precise mixing ratios, this leakage (and the variable mixing ratios that result) can render such assemblies useless. Unfortunately, manufacturing the gear pump components with ultra-tight tolerances to minimize such clearance often increases the cost of such assemblies to render them uneconomical. Moreover, very small clearances may result in high friction and difficulty in getter the motor started at low fluid pressures. Still further, prior art fluid motor and pump assemblies have typically been provided in configurations that limit their adaptability to varied mixing ratios due to a fixed relationship between the rate of rotation of a driving gear in the fluid motor and a driven gear in the fluid pump, and thus fail to provide a practical pump assembly enabling customized mixing proportions to be obtained. It would be advantageous to provide a means to adjust the flow proportion in a fast, easy manner. Accordingly, there remains a need for an apparatus that enables consistent, direct proportioning of flow of two liquids independent of the pressure and velocity of the driving liquid while enabling both fine and gross adjustment of the flow ratio in a simple manner, but of a sufficiently simplistic construction so as to maintain ease of manufacturing and low cost.